1. Field of the Invention
The present invention relates to a fringe field switching liquid crystal display (hereinafter, simply referred to as “FFS-LCD”), and more particularly to an FFS-LCD capable of preventing a misalignment of liquid crystal molecules caused by rubbing pressure in an FFS-LCD pixel structure, thereby preventing a display fault.
2. Description of the Prior Art
As generally known in the art, conventional thin-film liquid crystal displays (LCDs) are used as information display apparatuses, such as information display screens of portable terminals, displayers of notebook PCs, monitors of lap top computers, etc. Particularly, such liquid crystal displays have been widely used in various industrial fields in replacement of conventional CRT (cathode ray tube) monitors.
FIG. 1 is a plan view for illustrating a conventional FFS-LCD.
In addition, FIG. 2 is a view for showing a shape of a pixel electrode and a state of liquid crystal when an electric field is applied to the pixel electrode in the conventional FFS-LCD.
As shown in FIG. 1, the conventional FFS-LCD includes a pixel electrode 7, which is formed on the upper surface of a common electrode 4. The pixel electrode 7 has a slit pattern 7a. Herein, it is recommended that an edge portion of slit pattern 7a of the pixel electrode 7 should be formed in a constant angle of incline, but in actuality, as shown in FIG. 2, the edge portion of the slit pattern 7a of the pixel electrode 7 is formed in a curved line shape due to limitations of an exposure process.
In FIG. 1, reference numeral ‘2’ represents a gate line, reference numeral ‘3’ represents a data line, and reference numerals 5 and 6 represent source and drain electrodes respectively.
FIG. 3A is a view for showing a state of liquid crystal 8 when an electric field is not applied to the pixel electrode, and FIG. 3B is a view for showing a state of the liquid crystal 8 when a high electric field is applied to the pixel electrode. In addition, FIG. 30 is a view for showing a fault state of the liquid crystal 8, which is caused by a misalignment of liquid crystal 9 resulting from a high electric field and/or rubbing pressure.
Meanwhile, FIG. 4 is a view for explaining a problem which exists in the conventional FFS-LCD.
The operation of the conventional FFS-LCD having such a construction is as follows.
When any electric field is not formed at the common electrode and the pixel electrode, liquid crystal 8 is horizontally aligned as shown in FIG. 3A. In FIG. 3A, an arrow represents a rubbing direction.
Meanwhile, when a low electric field is applied, the liquid crystal is twisted by a few angles from the horizontal direction, and when a middle-degree electric field is applied, the liquid crystal is twisted by a little more degrees than those caused when the low electric field is applied.
In addition, as shown in FIGS. 2 and 3B, when a high electric field is applied to the liquid crystal 8, molecules of the liquid crystal 8 are twisted in such a manner that twisting angles of the molecules become enlarged more and more, to a right angle in maximum, as they reach the end part of an edge portion of the pixel electrode having a curved line shape due to an electric field interference between a black matrix (not shown) and the pixel electrode 7, so that the molecules of the liquid crystal 8 are vertically aligned at the end part of the edge portion. Since such an alignment may exert an influence on rubbing pressure, as shown in FIG. 3C, a circle phenomenon generated in the edge portion of the pixel electrode complicates the mobility of the liquid crystal according to applied voltages, thereby causing a fault due to a misalignment of liquid crystal when rubbing pressure is applied in a white gradation state.
That is, as shown in FIGS. 3C and 4, when rubbing pressure is applied under the white gradation state, the liquid crystal may not return to an initial alignment state, so a rubbing trace, that is, disclination lines 9 may occur.